Borosilicate or BORO for short is a formula of glass that is unique and very strong , I use Boro glass in almost all my beadwork , Boro is a more durable glass than most other formula.  Boro is also the formula used to produce Corning Pyrex Cookware. Borosilicate is able to withstand high temps that most commom glass formulas cannot withstand with breaking or fracturing.